Patients diagnosed with late-stage heart disease on average have 9 months to live, with standard deviation of survival = 18 months.

A pilot study finds that patients who are given comprehensive palliative care live on average for 12 months, with standard deviation of survival = 12 months.

How many patients will a follow-up study need, in order to have an 80% probability of being able to reject the null hypothesis that palliative care has no effect on survival, at a p-value of <= 5%?